Knotweed or Japanese bamboo is a rampant garden escape with no natural predator in this country. Even getting rid of its clippings is regulated under the 1990 Environmental Protection Act.
Discarded plants must be taken to licensed landfill sites and buried at least five metres deep. Link with environmental and ecological work at all levels: (http:info.ex.ac.ukknotweed or www.groundwork.org.uk).
* Pollen is linked to hay fever. The symptoms were described in the 19th century, but it's not caused by hay and there is no fever. It is the most common autoimmune disease, accounting for 2.5 per cent of visits to the GP and annual costs of more than pound;5m in medication. Pollen is produced by many trees in early March and by grasses between June and July. Each type is an antigen, so a person who is prone to allergies will make and store matching antibodies when first exposed to it; these attach themselves to the surface cells lining the nose. If the person breathes in this antigen again, it sticks to the antibodies and starts a cascade of complex events resulting in the sudden release of histamine and other chemicals.
It's the body's defences that orchestrate the symptoms, not the pollen itself.